Understanding the SDM

ML-Series cards use the forwarding engine and ternary content-addressable memory (TCAM) to implement high-speed forwarding. The high-speed forwarding information is maintained in TCAM. The SDM is the software subsystem that manages the switching information maintained in TCAM.

SDM organizes the switching information in TCAM into application-specific regions and configures the size of these application regions. SDM enables exact-match and longest-match address searches, which result in high-speed forwarding. SDM manages TCAM space by partitioning application-specific switching information into multiple regions.

TCAM identifies a location index associated with each packet forwarded and conveys it to the forwarding engine. The forwarding engine uses this location index to derive information associated with each forwarded packet.

Understanding SDM Regions

SDM partitions multiple application-specific regions and interacts with the individual application control layers to store switching information. The regions share the total available space. SDM consists of the following types of regions:

•Longest-match region—Each longest-match region consists of multiple buckets or groups of Layer 3 address entries organized in decreasing order by mask length. All entries within a bucket share the same mask value and key size. The buckets can change their size dynamically by borrowing address entries from neighboring buckets. Although the size of the whole application region is fixed, you can reconfigure it.

•Weighted-exact-match region—The weighted-exact-match region consists of exact-match-entries with an assigned weight or priority. For example, with QoS, multiple exact match entries might exist, but some have priority over others. The weight is used to select one entry when multiple entries match.

Configuring SDM

This section describes SDM region size and access control list (ACL) size configuration. The commands described in this section are unique to the switching software. Configuration changes take place immediately on the ML-100T-8 card.

Configuring SDM Regions

To configure SDM maximum size for each application region, perform the following procedure, beginning in global configuration mode: